1. Field of the Invention
The present invention relates to a particle size distribution measuring apparatus which detects a diffraction/scattering light generated by irradiating a laser beam onto a dispersing particle group, and measures a particle (grain) size distribution of the particle group on the basis of an intensity signal of the scattered light obtained by the detection.
2. Description of Related Art
In a particle size distribution measuring apparatus using a diffraction or scattering phenomenon of light by particles, an intensity distribution of diffraction light or scattering light, that is, a relationship between a diffraction or scattering angle and a light intensity is measured, and then, this measured result is subjected to operational processing based on a Fraunhofer diffraction theory or Mie scattering theory, and thereby, a particle size distribution of a sample particle is calculated (computed). The aforesaid particle size distribution measuring apparatus has been used for research and development of raw materials in a mining industrial field such as the cement or ceramic industry, and in ceramics, in particular.
In the development of new materials in the ceramic and polymer fields, a demand has been recently made to measure micro particles in a sub-micron region, and therefore, efforts have been made to develop instruments which can measure not only relatively large particles, but also particles in a sub-micron region.
An example of a particle size distribution measuring apparatus is disclosed in Japanese Examined Patent Publication (Kokoku) No. 6-43950. FIG. 4 is a view schematically showing a construction of the particle size distribution measuring apparatus disclosed in the above publication. In FIG. 4, a reference numeral 41 denotes a sample cell comprising a transparent container which contains a liquid (hereinafter, referred to as a sample solution) 42 prepared by dispersing a particle group of a target specimen for measurement in a medium liquid. A laser beam source 43 which is located on one side (rear side) of the cell 41 provides an enlarged parallel laser beam 44 from a beam expander (not shown) so as to irradiate the cell 41.
A collective (condenser) lens 45 is located on the other side (front side) of the cell 41, and a ring detector 46 is arranged on a focal position of the collective lens 41. The ring detector 46 is constructed in such a manner that a plurality of photo-sensors having a ring or semi-ring like light receiving surface having mutually different radius are coaxially arranged around an optical axis of the collective lens 45. Further, the ring detector 46 receives light scattered/diffracted at a relatively small angle off of the optical axis of the laser beam 44 which has been diffracted or scattered by the particles in the cell 41 for each scattering angle, and then, measures each respective light intensity.
An optical detector group 47 for wide-angle scattering light detects each light scattered/diffracted at a relatively large angle of the laser beam 44 which has been diffracted or scattered by the particles in the cell 41 for each scattering angle. Further, the optical detector group 47 for wide-angle scattering light is composed of the collective lens 45 and a plurality of photo-sensors 48 to 53 which are located at an angle different from the ring detector 46, and can detect a wide-angle scattering light which exceeds a predetermined angle by particles in the cell 41, in accordance with each located angle. More specifically, the photo-sensors 48 to 51 detect a forward scattering light, the photo-sensor 52 detects a side scattering light, and the photo-sensor 53 detects a backward scattering light.
A reference numeral 54 denotes a pre-amplifier for amplifying an output of the photo-sensors constituting the above ring detector 46, reference numerals 55 to 58 individually denote pre-amplifiers for amplifying each output of the photo-sensors 48 to 51 for forward scattering light, and reference numerals 59 and 60 individually denote pre-amplifiers for output of the photo-sensor 52 for side scattering light and the photo-sensor 53 for backward scattering light. A multiplexor 61 successively captures each output of the pre-amplifiers 54 to 60, and successively transmits the output to an A/D converter 62, and a computer 63 functions as a processor to which an output of the A/D converter 62 is inputted.
The computer 63 stores a program for processing the outputs converted into a digital signal (the digital data relative to light intensity) of the ring detector 46 and photo-sensor 48 to 53 on the basis of a known Fraunhofer diffraction theory or Mie scattering theory and determining a particle size distribution of the particle group.
In the aforesaid particle size distribution measuring apparatus, when sample liquid 42 is contained in the cell 41, the laser beam 44 is irradiated on the sample cell 41 from the laser beam source 43 and the laser beam 44 is diffracted or scattered by particles contained in the cell 41. Of the diffraction light or the scattering light, a light having a relatively small scattering angle is imaged on the ring detector 46 by means of the collective lens 45. In this case, the photo-sensor arranged on the outer peripheral side of the ring detector 46 receives a light having a larger scattering angle while the photo-sensor arranged on an inner peripheral side thereof receives light having a smaller scattering angle. Thus, a light intensity detected by the outer peripheral side photo-sensor reflects a particle quantity having a smaller particle size, and a light intensity detected by the inner peripheral side photo-sensor reflects a quantity of sample particle having a larger particle size. The light intensity detected by each photo-sensor is converted into an analog electric signal, and further, is inputted to the multiplexor 61 via the pre-amplifier 54.
On the other hand, of the laser beam 44 diffracted or scattered by the particles, a relatively large scattering angle light, which is not converged by the collective lens 45, is detected by means of the photo-sensors 48 to 53, and then, the light intensity distribution is measured. In this case, the photo-sensors 48 to 51 for forward scattering light, the photo-sensor 52 for side scattering light and the photo-sensor 53 for backward scattering light, successively detect scattering light from a particle having a small particle (grain) size. A light intensity detected by each of these photo-sensors 48 to 53 is converted into an analog electric signal, and then, is inputted to the multiplexor 61 via pre-amplifiers 55 to 60.
In the multiplexor 61, measurement data from the ring detector 46 and photo-sensors 48 to 53, that is, the analog electric signal is successively captured in a predetermined order. Then, the analog electric signal captured by the multiplexor 61 is made into a serial signal, and is successively converted into a digital signal by means of the A/D converter 62, and further, is inputted to the computer 63. The computer 63 processes light intensity data for each scattering angle obtained by each of the ring detector 46 and the photo-sensors 48 to 53 on the basis of a Fraunhofer diffraction theory and a Mie scattering theory.
As seen from the above description, in such a particle size distribution measuring apparatus, the light intensity distribution of the scattering light having a large particle size range is measured by means of the ring detector 46 while the light intensity distribution of the wide-angle scattering light having a small particle size range is measured by means of the photo-sensors 48 to 53. Then, the outputs of these ring detector 46 and photo-sensors 48 to 53 are processed by means of the computer 63, so that a particle size distribution of a particle group can be determined over a wide range from a relatively large particle size to a micro particle size.
However, the aforesaid particle size distribution measuring apparatus has the following problem. More specifically, in the particle size distribution measuring apparatus, a parallel beam is used as the laser beam 44 for irradiating the particle group contained in the cell 41; therefore, light having a small scattering angle is generated by particles having a relatively large particle size and the light is converged on the ring detector 46. For this reason, the collective lens 45 must be interposed between the cell 41 and the ring detector 46. As a result, this arrangement requires a long optical path length from the laser beam source 43 to the ring detector 46.
Moreover, the aforesaid arrangement of the collective lens 45 is a factor in causing the following problem. More specifically, in order to detect scattering light from a smaller particle (light having a large scattering angle), a plurality of photo-sensors 48 to 53 must be located so as to constitute the optical detector group 47 for wide-angle scattering light. In order to make the wide-angle scattering light incident upon these photo-sensors 48 to 53, there is a requirement of an accurate positional relationship between the collective lens 45 and the photo-sensors 48 to 53, in particular, the photo-sensors 48 to 51 for forward scattering light. Thus, in the aforesaid conventional particle size distribution measuring apparatus, an arrangement space must be widened so that the scattering light from the cell 41 can be securely incident upon all of photo-sensors 48 to 53.
As is evident from the above description, in the conventional particle size distribution measuring apparatus, the parallel laser beam 44 is irradiated on the cell 41, and the collective lens 45 is interposed between the cell 41 and the ring detector 46 and for this reason the apparatus must be made into a large size.
U.S. Pat. No. 5,737,078 discloses a flow cell for a cytoanalyzer and U.S. Pat. No. 5,796,480 is cited of interest.
The prior art is still seeking to provide an economical and compact portable measuring apparatus.